Acrylic resin composition, and optical film comprising same

ABSTRACT

The present invention relates to an acrylic copolymer resin containing: 1) an alkyl (meth)acrylate-based monomer; 2) a (meth)acrylate-based monomer containing an aliphatic ring and/or an aromatic ring; and 3) at least an imide-based monomer or a styrene-based monomer, to a resin composition containing said acrylic copolymer resin and a resin containing an aromatic ring and/or an aliphatic ring in the main chain thereof, to an optical film comprising said resin composition, and to a liquid crystal display device comprising said optical film. The optical film according to the present invention has excellent heat resistance, optical transparency, etc.

This application is a Continuation application of U.S. patentapplication Ser. No. 13/202,068, filed on Aug. 17, 2011, which is aNational Phase Entry of PCT Application No. PCT/KR2010/001019 filed onFeb. 18, 2010, which claims the benefit of Korean Patent Application No.10-2009-0013271, filed on Feb. 18, 2009, the disclosures of which areincorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an acrylic copolymer resin which hasexcellent heat resistance, to a resin composition including the acryliccopolymer resin, to an optical film which includes the resin compositionand has excellent heat resistance and optical transparency, and to aliquid crystal display device including the optical film.

BACKGROUND ART

Recently, display technologies using various methods such as a plasmadisplay panel (PDP), a liquid crystal display (LCD) and the like thatare used instead of a known brown tube in accordance with thedevelopment of optical technologies are suggested and sold. The higherproperties of the polymer material for displays are required. Forexample, in the case of the liquid crystal display, according to thedevelopment toward the thin film, the lightness, and enlargement of thescreen area, the wide viewing angle, the high contrast, the suppressionof change in image color tone according to the viewing angle and theuniformity of the screen display are particularly considered asimportant problems.

Therefore, various polymer films such as a polarizing film, aretardation film, a plastic substrate, a light guide plate and the likeare used, and various modes of liquid crystal displays such as twistednematic (TN), super twisted nematic (STN), vertical alignment (VA),in-plane switching (IPS) liquid crystal cells are developed. Since allof these liquid crystal cells have intrinsic liquid crystal alignment,they have intrinsic optical anisotropic property, and in order tocompensate the optical anisotropic property, a film in which aretardation function is provided by stretching various kinds of polymershas been suggested.

In detail, since a liquid crystal display device uses high birefringenceproperty and alignment of liquid crystal molecules, the birefringencesare different according to the viewing angle and thus the color andbrightness of the picture are changed. For example, since most liquidcrystal molecules that are used in a vertical alignment method have apositive retardation in a liquid crystal display surface, in order tocompensate this, a compensation film that has a negative retardation isrequired. In addition, light does not pass through the front sides oftwo polarizing plates that are perpendicular to each other, but if theangle is inclined, the light axes of two polarizing plates are notperpendicular to each other, thus light leakage occurs. In order tocompensate this, a compensation film having the in-plane retardation isrequired. In addition, display devices using a liquid crystal requireboth thickness retardation compensation and in-plane retardationcompensation in order to widen the viewing angle.

Requirements of the retardation compensation film are to control thebirefringence easily. However, the film birefringence is formed by abasic birefringence which belongs to the material and the orientation ofpolymer chains in the film. The orientation of the polymer chains ismostly forcibly performed by force applied from the outside or is causedby the intrinsic properties of the material, and the orientation methodof the molecules by the external force is to stretch a polymer filmuniaxially or biaxially.

In order to solve viewing angle problems of LCDs due to intrinsicbirefringence properties of the liquid crystal, N-TAC, V-TAC, and COPFilms have been recently used as a compensation film or a retardationfilm. However, these films are expensive and have problems in thatprocesses are complicated during the manufacture of the films.

DISCLOSURE Technical Problem

An aspect of the present invention provides an acrylic copolymer resinwhich maintains transparency and has better heat resistance than therelated-art.

Another aspect of the present invention provides a resin compositioncontaining the acrylic copolymer resin and a resin containing anaromatic ring and/or an aliphatic ring in the main chain thereof.

Another aspect of the present invention provides an optical film whichhas excellent heat resistance and optical transparency and contains theresin composition and a liquid crystal display device containing theoptical film.

Technical Solution

According to an aspect of the present invention, there is provided anacrylic copolymer resin containing 1) an alkyl (meth)acrylate-basedmonomer, 2) a (meth)acrylate-based monomer containing an aliphatic ringand/or an aromatic ring, and 3) at least one of an imide-based monomerand a styrene-based monomer.

According to another aspect of the present invention, there is provideda resin composition containing the acrylic copolymer resin and a resincontaining an aromatic ring and/or an aliphatic ring in the main chainthereof.

According to another aspect of the present invention, there is providedan optical film including the resin composition.

According to another aspect of the present invention, there is provideda liquid crystal display device including the optical film.

Advantageous Effects

An acrylic copolymer resin according to the present invention hasexcellent heat resistance while maintaining transparency. An opticalfilm manufactured by using a resin composition including the acryliccopolymer resin has excellent transparency and heat resistance and isexcellent in processability, adhesion, retardation property, anddurability.

DESCRIPTION OF DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1 to 4 illustrate examples of applying an optical film accordingto an embodiment of the present invention to a liquid crystal displaydevice.

BEST MODE

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

Hereinafter, the present invention will be described in more detail.

According to an aspect of the present invention, there is provided anacrylic copolymer resin containing 1) an alkyl (meth)acrylate-basedmonomer; 2) a (meth)acrylate-based monomer containing an aliphatic ringand/or an aromatic ring; and 3) at least one of an imide-based monomerand a styrene-based monomer.

A copolymer resin including a monomer used herein means that a monomeris polymerized and included as a repeating unit in the copolymer resin.

The acrylic copolymer may be a block copolymer or a random copolymer,but it is not limited thereto.

The acrylic copolymer may be a three-membered copolymer containing analkyl (meth)acrylate-based monomer; a (meth)acrylate-based monomercontaining an aliphatic ring and/or an aromatic ring; and astyrene-based monomer; a four-membered copolymer additionally containingan imide-based monomer thereto; and a three-membered monomer containingan alkyl (meth)acrylate-based monomer; a (meth)acrylated-based monomercontaining an aliphatic ring and/or an aromatic ring; and an imide-basedmonomer.

In the acrylic copolymer resin, the alkyl (meth)acrylate-based monomerand the (meth)acrylate-based monomer are preferably present in an amountof 30 wt % to 90 wt % and more than 0 wt % and 50 wt % or less,respectively. In addition, the imide-based monomer and the styrene-basedmonomer are preferably present in an amount of 0.1 wt % to 50 wt % and0.1 wt % to 50 wt %, respectively, and these may be included in theacrylic copolymer alone or in combination.

In the acrylic copolymer resin, the alkyl(meth)acrylate-based monomermeans both an alkylacrylate-based monomer and an alkylmethacrylate-based monomer. The alkyl group in thealkyl(meth)acrylate-based monomer has preferably a carbon number of 1 to10 and more preferably 1 to 4, and may be a methyl group or an ethylgroup. The alkyl methacrylate-based monomer may be more preferablymethylmethacrylate, but it is not limited thereto.

In the acrylic copolymer resin, the alkyl methacrylate-based monomer ispresent preferably in an amount of 30 wt % to 90 wt % and morepreferably 50 wt % to 90 wt %. When the alkyl methacrylate-based monomeris present in the range, heat resistance may be maintained while itstransparency is excellent.

The (meth)acrylate-based monomer containing an aliphatic ring and/or anaromatic ring in the acrylic copolymer resin serves to increase the heatresistance of the acrylic copolymer resin according to the presentinvention, and may be, for example, a cycloalkyl (meth)acrylate-basedmonomer or an aryl (meth)acrylate-based monomer.

A cycloalkyl group of the cycloalkyl (meth)acrylate-based monomer haspreferably a carbon number of 4 to 12, more preferably 5 to 8, and mostpreferably a cyclohexyl group. In addition, an aryl group of thearyl(meth)acrylate-based monomer has preferably a carbon number of 6 to12, and most preferably is a phenyl group.

Specific examples of the (meth)acrylate-based monomer containing analiphatic ring and/or an aromatic ring are preferably cyclopentylmethacrylate, cyclohexyl methacrylate, benzyl methacrylate, cyclohexylacrylate, 2-phenoxyethyl acrylate, 3,3,5-trimethylcyclohexylmethacrylate, 4-t-butylcyclohexyl methacrylate, 3-cyclohexylpropylmethacrylate, phenyl methacrylate, 4-t-butylphenyl methacrylate,4-methoxyphenyl methacrylate, 1-phenylethyl methacrylate, 2-phenylethylacrylate, 2-phenylethyl methacrylate, 2-phenoxyethyl methacrylate,2-naphthyl methacrylate, and the like, and may be preferably cyclohexylmethacrylate or phenyl methacrylate, but it is not limited thereto.

In the acrylic copolymer resin, the (meth)acrylate-based monomercontaining an aliphatic ring and/or an aromatic ring is presentpreferably in an amount of more than 0 wt % and 50 wt % or less, morepreferably more than 0 wt % and 30 wt % or less, and most preferably 5wt % to 30 wt %. When the (meth)acrylate-based monomer containing analiphatic ring and/or an aromatic ring is present in the range, heatresistance may be sufficiently secured.

In the acrylic copolymer, the imide-based monomer means a monomerincluding an imide group, and may be, for example, maleimides, and thelike. Among them, maleimides substituted with a cycloalkyl group or anaryl group may be used in order to increase the heat resistance of theacrylic copolymer.

A cycloalkyl group which may be substituted in the imide-based monomeris preferably a cycloalkyl group with a carbon number of 3 to 15, andmore preferably a cyclohexyl group. In addition, an aryl group which maybe substituted in the imide-based monomer is an aryl group with a carbonnumber of 6 to 15, and more preferably a phenyl group.

Specific examples of the imide-based monomer may beN-cyclohexylmaleimide, N-phenylmaleimide, N-chlorophenylmaleimide,N-methylphenylmaleimide, N-naphthylmaleimide, N-hydroxyphenylmaleimide,N-methoxyphenylmaleimide, N-carboxyphenylmaleimide,N-nitrophenylmaleimide, N-tribromophenylmaleimide, and the like. Thesemonomers may be used alone or in combination thereof. Among thesemonomers, N-cylcohexylmaleimide or N-phenylmaleimide is particularlypreferable, but it is not limited thereto.

In the acrylic copolymer resin, the imide-based monomer is presentpreferably in an amount of 0.1 wt % to 50 wt %, and more preferably 1 wt% to 20 wt %. When the imide-based monomer is present in the range, itis preferable because the degradation of mechanical strength may beminimized while heat resistance is secured.

In the acrylic copolymer, the styrene-based monomer means a monomercontaining a styrene group, and may be, for example, styrene,α-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene,2,5-dimethylstyrene, 2-methyl-4-chlorosytrene, 2,4,6-trimethylstyrene,cis-β-methylstyrene, trans-β-methylstyrene, 4-methyl-α-methylstyrene,4-fluoro-α-methylstyrene, 4-chloro-α-methylstyrene,4-bromo-α-methylstyrene, 4-t-butylstyrene, 2-fluorostyrene,3-fluorostyrene, 4-fluorostyrene, 2,4-difluorostyrene,2,3,4,5,6-pentafluorostyrene, 2-chlorostyrene, 3-chlorostyrene,4-chlorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene,octachlorostyrene, 2-bromostyrene, 3-bromostyrene, 4-bromostyrene,2,4-dibromostyrene, α-bromostyrene, β-bromostyrene, 2-hydroxystyrene,4-hydroxystyrene, and the like. Among them, α-methylstyrene is mostpreferable in terms of polymerizability and heat resistance, but it isnot limited thereto.

In the acrylic copolymer resin, the styrene-based monomer is presentpreferably in an amount of 0.1 wt % to 50 wt %, and more preferably 1 wt% to 20 wt %. When the styrene-based monomer is present in the range, itis preferable because the degradation of mechanical strength may beminimized while heat resistance is secured.

In addition, the acrylic copolymer resin preferably has a molecularweight of 50,000 to 500,000 in terms of heat resistance, processability,and productivity.

The acrylic copolymer resin has a glass transition temperature ofpreferably 120° C. or more, and more preferably 130° C. or more.Although the glass transition temperature of the acrylic copolymer resinis not particularly limited, it may be 200° C. or less.

According to another aspect of the present invention, there is provideda resin composition containing the acrylic copolymer resin and a resincontaining an aromatic ring and/or an aliphatic ring in the main chainthereof.

In the resin composition, the resin containing an aromatic ring and/oran aliphatic ring in the main chain thereof may be, for example, apolycarbonate-based resin, a polyarylate-based resin,polynaphthalene-based resin, a polynorbornene-based resin, and the like.The resin may be a polycarbonate-based resin, but it is not limitedthereto.

In the resin composition, a weight ratio of the acrylic copolymer resinto the resin containing an aromatic ring and/or an aliphatic ring in themain chain thereof is preferably 60 to 99.9:0.1 to 40, and morepreferably 70 to 99:1 to 30.

The resin composition may be prepared by blending the acrylic copolymerresin with the resin containing an aromatic ring and/or an aliphaticring in the main chain thereof according to a method well known in theart, such as a compounding method, and an additive well known in theart, such as a colorant, a flame retardant, an enhancer, a filler, a UVstabilizer, an antioxidant, and the like, may be included in an amountof 0.001 to 70 parts by weight.

The resin composition has a glass transition temperature of preferably110° C. and more preferably 120° C. The glass transition temperature ofthe resin composition is not particularly limited, but it may be 200° C.or less.

In addition, the resin composition preferably has a weight averagemolecular weight of 50,000 to 500,000 in terms of heat resistance,sufficient processability, productivity, and the like.

According to another aspect of the present invention, there is provided3) an optical film including the resin composition.

An optical film according to the present invention may have differentretardation values according to the content of a resin containing anaromatic ring and/or an aliphatic ring in the main chain thereof, andthus may be used as a retardation compensation film or a protectivefilm.

The retardation compensation film may be used on the VA mode type or theTN mode type according to the retardation value. An optical filmaccording to the present invention has an in-plane retardation value(R_(in)) of 30 nm to 80 nm and a thickness retardation value (R_(th)) of−50 nm to −300 nm, and may be used as a VA mode type retardationcompensation film in this case. In addition, an optical film accordingto the present invention may have an in-plane retardation value (R_(in))of 150 nm to 200 nm and a thickness retardation value (R_(th)) of −90 nmor less, that is, an absolute value of 90 or more of the thicknessretardation value, and may be used as a TN mode type retardationcompensation film in this case. When the TN mode type retardationcompensation film is used, the thickness retardation value (R_(th)) ismore preferably in a range of −90 nm to −150 nm.

As an example, when the resin containing an aromatic ring and/or analiphatic ring in the main chain thereof is present in an amount of 10wt % to 40 wt %, the optical film may have an in-plane retardation value(R_(in)) of 30 nm to 80 nm and a thickness retardation value (R_(th)) of−50 nm to −300 nm. In this case, the optical film according to thepresent invention may be used as a VA mode type retardation compensationfilm.

As another example, when the resin containing an aromatic ring and/or analiphatic ring in the main chain thereof is present preferably in anamount of 0.1 wt % to 10 wt % and more preferably 1 wt % to 5 wt %, theoptical film may have an in-plane retardation value (R_(in)) of 0 nm to10 nm, preferably 0 nm to 5 nm, and more preferably about 0 nm, and athickness retardation value (R_(th)) of −10 nm to 10 nm, preferably −5nm to 5 nm, and more preferably about 0 nm. In this case, the opticalfilm according to the present invention may be used as a polarizerprotective film.

An example in which the optical film according to the present inventionis used as a protective film is shown in FIG. 2. Although protectivefilms provided on both sides of two polarizing plates are all opticalfilms according to the present invention, but a related-art protectivefilm may be used in at least one of the protective films.

The 3) optical film may be manufactured into a film by a method wellknown in the art, such as a solution cast method or an extrusion method,using the 2) resin composition, and the solution cast method may bepreferably used among them.

The method may further include stretching the film manufactured as aboveuniaxially or biaxially, and the film may be manufactured by adding amodifier, if necessary.

The stretching process may be performed by using any one of a machinedirection (MD) stretching and a transverse direction (TD) stretching orboth of the machine direction stretching and the transverse directionstretching. When both of the machine direction stretching and thetransverse direction stretching are performed, any one of them may befirst performed and then the other may be performed, or both of them maybe performed simultaneously. The stretching may be performed through asingle step or through multi-steps. When the stretching is performed inthe machine direction, the stretching may be performed by using adifference in speed between rolls, and when the stretching is performedin the transverse direction, the tenter may be used. The rail initiatingangle of the tenter is 10° or less, a bowing phenomenon that occurs whenthe transverse direction stretching is performed is suppressed, and theangle of the optical axis is regularly controlled. By performing thetransverse direction stretching through multi-steps, the suppressionphenomenon of the bowing phenomenon may be obtained.

The stretching may be performed at a temperature in the range of(Tg−−20° C.) to (Tg+30° C.) when the glass transition temperature of theresin composition is Tg. The glass transition temperature means a rangefrom a temperature at which storage elasticity of the resin compositionstarts to be reduced and the loss elasticity starts to be larger thanthe storage elasticity to a temperature at which alignment of thepolymer chain is loosened and removed. The glass transition temperaturemay be measured by using a differential scanning calorimeter (DSC). Thetemperature during the stretching process is more preferably the glasstransition temperature of the film.

In the case of a small stretching machine (Universal testing machine,Zwick Z010), it is preferable that the stretching rate is in the rangeof 1 to 100 mm/min. In the case of a pilot stretching machine, it ispreferable that the stretching rate is in the range of 0.1 to 2 mm/min.In addition, it is preferable that the film is stretched by using astretching ratio in the range of 5 to 300%.

Retardation properties of the optical film according to the presentinvention may be controlled by stretching the optical film uniaxially orbiaxially by the method described above.

The optical film manufactured as above preferably has an in-planeretardation value of 0 nm to 200 nm, represented by the followingMathematical Formula 1 and a thickness retardation value of 10 nm to−300 nm, represented by the following Mathematical Formula 2.R _(in)=(n _(x) −n _(y))×d  [Mathematical Formula 1]R _(th)=(n _(z) −n _(y))×d  [Mathematical Formula 2]

In Mathematical Formulas 1 and 2, n_(x) is a refractive index in adirection in which the index is largest, in the film plane,

n_(y) is a refractive index in a direction perpendicular to the n_(x)direction, in the film plane,

n_(z) is a refractive index in a thickness direction, and d is a filmthickness.

In the optical film according to the present invention, the in-planeretardation value and the thickness retardation value may be controlledaccording to the content of the resin containing an aromatic ring and/oran aliphatic ring in the main chain thereof. For example, the opticalfilm according to the present invention may have an in-plane retardationvalue (R_(in)) of 20 nm to 80 nm and a thickness retardation value(R_(th)) of −50 nm to −300 nm. In this case, the optical film accordingto the present invention may be used as a VA mode type retardationcompensation film. In addition, the optical film according to thepresent invention may have an in-plane retardation value (R_(in)) of 0nm to 10 nm, preferably 0 nm to 5 nm, more preferably about 0 nm, and athickness retardation value (R_(th)) of −10 nm to 10 nm, preferably −5nm to 5 nm, and more preferably about 0 nm. In this case, the opticalfilm according to the present invention may be used as a polarizerprotective film.

When the optical film according to the present invention is applied to aliquid crystal display device, the film may be provided only on one side(one-piece type) of a liquid crystal panel and each provided on bothsides. Although the one-piece type is shown in FIG. 3 and the two-piecetype is shown in FIG. 4, the scope of the present invention is notlimited thereto.

When the optical film according to the present invention is providedonly on one side of a liquid crystal panel, the optical film has anin-plane retardation value (R_(in)) of 30 nm to 80 nm, preferably 35 nmto 70 nm, and more preferably about 40 nm to about 60 nm, and athickness retardation value (R_(th)) of −270 nm or less, that is, it ispreferable that an absolute value of the thickness retardation value is270 or more.

When the optical films according to the present invention are providedon each side of a liquid crystal panel, the optical films have anin-plane retardation value (R_(in)) of 30 nm to 80 nm, preferably 35 nmto 70 nm, and more preferably about 40 nm to about 60 nm, and athickness retardation value (R_(th)) of −100 nm or less, that is, it ispreferable that an absolute value of the thickness retardation value is100 or more.

The optical film according to the present invention has a photoelasticcoefficient lower than those of related-art TAC films. The optical filmaccording to the present invention may have a photoelastic coefficientof 10 or less, preferably 8 or less, more preferably 0.1 to 7, and mostpreferably 0.5 to 6.

The brittleness of the optical film according to the present inventionmay be measured by dropping an iron sphere with a diameter of 15.9 mmand a weight of 16.3 g on a test film to measure the height of a holeproduced on the film. The optical film according to the presentinvention has a height of preferably 600 nm and more preferably 700 nm.

The optical film according to the present invention has a haze value ofpreferably 1% or less, more preferably 0.5% or less, and most preferably0.1% or less.

According to another aspect of the present invention, there is provideda liquid crystal display device including the optical film.

The liquid crystal display device may be a vertical alignment (VA) modetype or TN mode type liquid crystal display device. Although the VA modetype will be usually described, the optical film according to thepresent invention may be also applied to a TN mode type liquid crystaldisplay device.

In the VN mode type liquid crystal display device, an optical film maybe used to compensate the viewing angle, and has two requirements to becompensated. One of them is a light leakage compensation in twopolarizing plates due to the characteristics that the absorption axis ofthe polarizing plates is not apparently perpendicular to each other whena liquid crystal display device is obliquely observed. The other is anecessary compensation because the degradation of the contrast is shownby the occurrence of a light leakage from a cell during black colordisplay due to an increase in birefringence of a liquid crystal moleculewhen a VA cell is observed from the oblique direction.

A polarizer to be combined with an optical film consists of a uniaxiallystretched polyvinylalcohol film containing a dichroic dye, and is veryfragile. Thus, the polarizer has low durability to temperature andmoisture and is combined with protective films. If an optical film maybe directly adhered to a polarizer instead of a protective film, anoptical film integrated with a thin retardation film corresponding to afirst layer of a protective film may be obtained.

Cellulose derivatives are excellent in water permeability and thusadvantageous in that moisture contained in a polarizer may bevolatilized through a film in the manufacturing process of a polarizingplate. However, dimensional changes and changes in optical propertiesaccording to moisture absorption under high temperature and highmoisture atmosphere are relatively large. When the humidity is changedaround room temperature, a change in retardation values is so large thatthere is a limitation on improvement of a stable viewing angle. Thus,the durability of optical properties of a polarizing plate may bedeteriorated.

Furthermore, polycarbonate-based materials have such a high glasstransition temperature that it is necessary to perform a stretchingprocess at high temperature and an optical switch by stress occurs dueto a high photoelastic coefficient. When a norbornene-based isstretched, stress may be high during the stretching or stress may not beuniform during the stretching. These problems may be solved by employingan acryl-based retardation film which has excellent viewing anglecompensation effects and has low change in retardation values even underenvironmental changes.

A liquid crystal display device including one or two or more opticalfilms according to the present invention will be described in moredetail as follows.

In a liquid crystal display device including a liquid crystal cell andfirst and second polarizing plates each provided on both sides of theliquid crystal cell, an optical film may be provided between the liquidcrystal cell and the first polarizing plate and/or the second polarizingplate. That is, an optical film may be provided between the firstpolarizing plate and the liquid crystal cell, and one or two or moreoptical films may be provided between the second polarizing plate andthe liquid crystal cell, or between the first polarizing plate and theliquid crystal cell and between the second polarizing plate and theliquid crystal cell.

The first and second polarizing plates may include a protective film onone surface or both surfaces. The internal protective film may be atriacetate cellulose (TAC) film, a polynorbornene-based film prepared byring opening metathesis polymerization (ROMP), a ring opening metathesispolymerization followed by hydrogenation (HROMP) polymer film, which isobtained by hydrogenating a ring opening metathesis polymerizedcycloolefine-based polymer, a polyester film, and a polynorbonene-basedfilm prepared by addition polymerization. Besides, a film of atransparent polymer material, and the like may be used, but it is notlimited thereto.

In addition, the present invention includes a polarizing film andprovides an integrated type polarizing plate including an optical filmaccording to the present invention as a protective film on one surfaceor both surfaces of the polarizing film.

When an optical film according to the present invention is provided onlyon one surface of a polarizing film, a protective film known in the artmay be provided on the other surface.

A film consisting of polyvinyl alcohol (PVA) including iodine or adichroic pigment may be used as the polarizing film. The polarizing filmmay be prepared by dyeing iodine or a dichroic pigment on a PVA film,but a manufacturing method thereof is not particularly limited. In thepresent specification, the polarizing film means a state that does notinclude the protective film, and the polarizing plate means a state thatincludes the polarizing film and the protective film.

In an integrated type polarizing plate of the present invention, theprotective film and the polarizing film may be combined by using amethod that is known in the art.

For example, the combination of the protective film and the polarizingfilm may be performed by an adhesion method using a bonding agent. Thatis, a bonding agent is first coated on the surface of a protective filmof the polarizing film or a PVA film as a polarizing film by using aroll coater, a gravure coater, a bar coater, a knife coater, or acapillary coater. Before the bonding agent is completely dried, theprotective film and the polarizing film are heat-pressed with acombination roll or pressed at room temperature to be combined. When ahot-melt bonding agent is used, a heat-pressing roll should be used.

An available bonding agent during combination of the protective film andthe polarizing plate may be a one-component or a two-component PVAbonding agent, a polyurethane-based bonding agent, an epoxy-basedbonding agent, a styrene-butadiene rubber-based (SBR-based) bondingagent, or a hot-melt bonding agent, but it is not limited thereto. Whenthe polyurethane-based bonding agent is used, it may preferably be abonding agent prepared using an aliphatic isocyanate compound which isnot yellowed by light. When a one-component or two-component bondingagent for dry laminate or a bonding agent with a relatively lowreactivity of isocyanate with hydroxy group is used, a solution bondingagent diluted with an acetate-based solvent, a ketone-based solvent, anether-based solvent, or an aromatic solvent may be also used. Theviscosity of the bonding agent is preferably 5,000 cps or less. Thesebonding agents may have excellent storage stability and lighttransmittance of 90% or more at 400-800 nm.

An adhesive may be also used as long as it may show sufficient adhesion.Preferably, the adhesive is sufficiently cured by heat or ultravioletradiation after combination to increase the mechanical strength thereofto the level of a bonding agent such that its adhesion is too high topeel it off without destroying one or both sides of film to which theadhesive is attached. Specific examples of an available adhesive includenatural rubber, synthetic rubber or elastomer, vinyl chloride/a vinylacetate copolymer, polyvinylalkylether, polyacrylate, or modifiedpolyolefinic adhesive, which have good optical transparency, andhardened adhesives produced by adding a curing agent thereto.

In addition, the present invention provides a liquid crystal displaydevice including the integrated type polarizing plate. The structure ofa liquid crystal display device according to the present invention isshown in FIG. 1, but the scope of the present invention is not limitedthereto.

When a liquid crystal display device according to the present inventionincludes the integrated type polarizing plate described above, one ormore optical films according to the present invention may beadditionally included between a polarizing plate and a liquid crystalcell.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

MODE FOR INVENTION

Hereinafter, preferred Examples will be described to aid inunderstanding of the present invention. The following Examples onlyillustrate the present invention but the scope of the present inventionis not limited thereto.

Evaluation methods of physical properties in the present invention areas follows.

1. Weight average molecular weight (Mw): measured by dissolving a resinprepared in tetrahydrofuran and using a gel chromatography (GPC).

2. Tg (Glass transition Temperature): measured by using a DifferentialScanning calorimeter (DSC) from TA Instrument.

3. Retardation value (R_(in)/R_(th)): measured by performing thestretching at glass transition temperature of the film and using AxoScanfrom Axometrics.

4. Haze value (transparency): measured by using a HAZEMETER HM-150 fromMurakami color Research Laboratory.

EXAMPLE Example 1

A resin was manufactured with 82 wt % of methyl methacrylate, 10 wt % ofcyclohexyl methacrylate, 3 wt % of alpha-methyl styrene, and 5 wt % ofN-cyclohexyl maleimide. The glass transition temperature and molecularweight of the resin prepared were measured and a resin with a glasstransition temperature of 135° C. and a molecular weight of 80,000 wasobtained. The resin and polycarbonate were mixed at a weight ratio of90:10 and compounded to prepare a final resin composition. The resincomposition was prepared into a film by a solution casting method, astretching was performed at the glass transition temperature thereof,and a retardation value of the film was measured. As a result, thein-plane retardation value/thickness retardation value and the Hazevalue were 48/−130 and 0.1, respectively.

Example 2

A resin was manufactured with 65 wt % of methyl methacrylate, 10 wt % ofcyclohexyl methacrylate, 10 wt % of styrene, and 15 wt % of N-cyclohexylmaleimide. The glass transition temperature and molecular weight of theresin prepared were measured and a resin with a glass transitiontemperature of 130° C. and a molecular weight of 90,000 was obtained.The resin and polycarbonate were mixed at a weight ratio of 90:10 andcompounded to prepare a final resin composition. The resin compositionwas prepared into a film by a solution casting method, a stretching wasperformed at the glass transition temperature thereof, and a retardationvalue of the film was measured. As a result, the in-plane retardationvalue/thickness retardation value and the Haze value were 43/−125 and0.1, respectively.

Example 3

A resin was manufactured with 65 wt % of methyl methacrylate, 20 wt % ofcyclohexyl methacrylate, 5 wt % of alpha-methyl styrene, and 10 wt % ofphenyl maleimide. The glass transition temperature and molecular weightof the resin prepared were measured and a resin with a glass transitiontemperature of 131° C. and a molecular weight of 80,000 was obtained.The resin and polycarbonate were mixed at a weight ratio of 90:10 andcompounded to prepare a final resin composition. The resin compositionwas prepared into a film by a solution casting method, a stretching wasperformed at the glass transition temperature thereof, and a retardationvalue of the film was measured. As a result, the in-plane retardationvalue/thickness retardation value and the Haze value were 40/−115 and0.1, respectively.

Example 4

A resin was manufactured with 82 wt % of methyl methacrylate, 10 wt % ofbenzyl methacrylate, 3 wt % of alpha-methyl styrene, and 5 wt % ofN-cyclohexyl maleimide. The glass transition temperature and molecularweight of the resin prepared were measured and a resin with a glasstransition temperature of 130° C. and a molecular weight of 90,000 wasobtained. The resin and polycarbonate were mixed at a weight ratio of90:10 and compounded to prepare a final resin composition. The resincomposition was prepared into a film by a solution casting method, astretching was performed at the glass transition temperature thereof,and a retardation value of the film was measured. As a result, thein-plane retardation value/thickness retardation value and the Hazevalue were 48/−140 and 0.1, respectively.

Example 5

A resin was manufactured with 80 wt % of methyl methacrylate, 10 wt % ofcyclohexyl methacrylate, and 10 wt % of alpha-methyl styrene. The glasstransition temperature and molecular weight of the resin prepared weremeasured and a resin with a glass transition temperature of 130° C. anda molecular weight of 75,000 was obtained. The resin and polycarbonatewere mixed at a weight ratio of 90:10 and compounded to prepare a finalresin composition. The resin composition was prepared into a film by asolution casting method, a stretching was performed at the glasstransition temperature thereof, and a retardation value of the film wasmeasured. As a result, the in-plane retardation value/thicknessretardation value and the Haze value were 55/−95 and 0.1, respectively.

Example 6

A resin was manufactured with 80 wt % of methyl methacrylate, 15 wt % ofcyclohexyl methacrylate, and 5 wt % of N-cyclohexyl maleimide. The glasstransition temperature and molecular weight of the resin prepared weremeasured and a resin with a glass transition temperature of 118° C. anda molecular weight of 85,000 was obtained. The resin and polycarbonatewere mixed at a weight ratio of 90:10 and compounded to prepare a finalresin composition. The resin composition was prepared into a film by asolution casting method, a stretching was performed at the glasstransition temperature thereof, and a retardation value of the film wasmeasured. As a result, the in-plane retardation value/thicknessretardation value and the Haze value were 43/−90 and 0.1, respectively.

Comparative Example 1

A resin was manufactured with 80 wt % of methyl methacrylate and 20 wt %of cyclohexyl methacrylate. The glass transition temperature andmolecular weight of the resin prepared were measured and a resin with aglass transition temperature of 119° C. and a molecular weight of100,000 was obtained. The resin and polycarbonate were mixed at a weightratio of 90:10 and compounded to prepare a final resin composition. Theresin composition was prepared into a film by a solution casting method,a stretching was performed at the glass transition temperature thereof,and a retardation value of the film was measured. As a result, thein-plane retardation value/thickness retardation value and the Hazevalue were 35/−100 and 0.1, respectively.

The Examples and Comparative Example are summarized in the followingTable 1 and Table 2.

TABLE 1 Monomer (wt %) Styrene- Imide- MMA CHMA BzMA based based Example1 82 10 — AMS 3 CHMI 5 Example 2 65 10 — SM 10 CHMI 15 Example 3 65 20 —AMS 5 PMI 10 Example 4 82 — 10 AMS 3 CHMI 5 Example 5 80 10 — AMS 10 —Example 6 80 15 — — CHMI 5 Comparative 80 20 — — — Example 1 MMA: Methylmethacrylate CHMA: Cyclohexyl methacrylate BzMA: Benzyl methacrylateAMS: Alpha-methyl styrene SM: Styrene CHMI: N-cyclohexyl maleimide PMI:Phenyl maleimide

TABLE 2 Haze (%) Tg (° C.) Mw R_(in) (nm) R_(th) (nm) Example 1 0.1 13580,000 48 −130 Example 2 0.1 130 90,000 43 −125 Example 3 0.1 131 80,00040 −115 Example 1 0.1 130 90,000 48 −140 Example 1 0.1 130 75,000 55 −95Example 1 0.1 118 85,000 43 −90 Example 1 0.1 119 100,000 35 −100

Examples 7 to 21

A copolymer resin with a monomer composition as in the following Table 3was prepared, mixed with polycarbonate, and compounded to prepare afinal resin composition. The resin composition was prepared into a filmby a solution casting method, a stretching was performed at the glasstransition temperature thereof, and a retardation value of the film wasmeasured. Physical properties of the film prepared are shown in thefollowing Table 4.

TABLE 3 Monomer (wt %) Acrylate (meth)acrylate- resin PC based monomerStyrene- Imide- (parts (parts Misci- MMA including a ring based based byweight) by weight) bility Example 7 80 CHMA 10 — PMI 10 90 10 0 Example8 60 CHMA 20 — CHMI 15 88 12 0 Example 9 82 CHMA 10 AMS 3 PMI 5 88 12 0Example 10 60 CHMA 15 SM 10 CHMI 15 90 10 0 Example 11 80 BzMA 10 — PMI10 90 10 0 Example 12 82 BzMA 10 AMS 3 CHMI 5 88 12 0 Example 13 75 BzMA15 SM 10 — 90 10 0 Example 14 85 PhMA 10 — PMI 5 80 20 0 Example 15 70PhMA 20 — CHMI 10 75 25 0 Example 16 75 PhMA 10 AMS 3 PMI 5 80 20 0Example 17 65 PhMA 15 SM 8 PMI 12 77 23 0 Example 18 80 CHMA 10 — PMI 1098 2 0 Example 19 85 PhMA 10 — CHMI 5 98.5 1.5 0 Example 20 82 CHMA 10AMS 3 PMI 5 99 1 0 Example 21 75 PhMA 10 SM 5 CHMI 10 99.2 0.8 0Comparative 80 CHMA 20 — — 90 10 0 Example 1 PhMA: Phenyl methacrylate

TABLE 4 Photoelastic Tg Mw Rin Rth coefficient Example 7 130 80000 40−111 3.8 Example 8 132 90000 50 −121 4.2 Example 9 135 80000 52 −125 4.1Example 10 130 85000 42 −105 3.9 Example 11 128 85000 41 −100 4 Example12 130 80000 51 −186 4.3 Example 13 128 80000 50 −99 4 Example 14 13095000 56 −275 5.5 Example 15 131 100000 65 −296 6 Example 16 133 8000060 −263 5.2 Example 17 130 90000 59 −273 5.7 Example 18 130 80000 1.3−2.1 1.1 Example 19 129 95000 0.5 −1.5 0.9 Example 20 130 85000 1.5 −0.60.6 Example 21 133 90000 0.3 −0.7 0.5 Comparative 119 100000 45 −100 4Example 1

The brittlenesses of the optical films prepared in Examples 12 to 14 maybe measured by dropping an iron sphere with a diameter of 15.9 mm and aweight of 16.3 g on the test films to measure the heights of holesproduced on the films.

TABLE 5 Example 12 Example 13 Example 14 Height of a hole 740 mm 700 mm710 mm produced on a film

The invention claimed is:
 1. An optical film comprising a resincomposition comprising: an acrylic copolymer; and a resin comprising anaromatic ring and/or an aliphatic ring in the main chain thereof,wherein the acrylic copolymer comprises: an alkyl (meth)acrylate-basedmonomer in an amount of 30 wt. % to 90 wt. %; a (meth)acrylate-basedmonomer comprising an aliphatic ring and/or an aromatic ring in anamount of more than 0 wt. % and 50 wt. % or less; an imide-based monomerin an amount of 1 wt. % to 20 wt. %; and a styrene-based monomer in anamount of 0.1 wt. % to 50 wt. %, and wherein a glass transitiontemperature (Tg) of the acrylic copolymer is 120° C. or more and 200° C.or less, and wherein the resin comprising an aromatic ring and/or analiphatic ring in the main chain thereof is selected from the groupconsisting of a polycarbonate-based resin, a polyacrylate-based resin, apolynaphthalene-based resin, and a polynorbornene-based resin.
 2. Theoptical film of claim 1, wherein the resin composition has a weightratio of the acrylic copolymer resin to the resin comprising an aromaticring and/or an aliphatic ring in the main chain thereof of 60 to99.9:0.1 to
 40. 3. The optical film of claim 1, wherein a glasstransition temperature of the resin composition is 110° C. or more. 4.The optical film of claim 1, wherein the optical film is a retardationcompensation film or a protective film.
 5. The optical film of claim 4,wherein the retardation compensation film is for a VA mode liquidcrystal display device or a TN mode liquid crystal display device. 6.The optical film of claim 1, wherein the optical film has an in-plainretardation value of −5 nm to 200 nm, represented by the followingMathematical Formula 1:R _(in)=(n _(x) −n _(y))×d  [Mathematical Formula 1] where, n_(x) is arefractive index in a direction in which the index is largest, in thefilm plane, n_(y) is a refractive index in a direction perpendicular tothe n_(x) direction, in the film plane, and d is a film thickness. 7.The optical film of claim 1, wherein the optical film has a thicknessretardation value of 5 nm to −300 nm, represented by the followingMathematical Formula 2:R _(th)=(n _(z) −n _(y))×d  [Mathematical Formula 2] where, n_(x) is arefractive index in a direction in which the index is largest, in thefilm plane, n_(y) is a refractive index in a direction perpendicular tothe n_(x) direction, in the film plane, n_(z) is a refractive index in athickness direction, and d is a film thickness.
 8. The optical film ofclaim 1, wherein the optical film has an in-plane retardation value of20 nm to 80 nm, represented by the following Mathematical Formula 1, anda thickness retardation value of −50 nm to −300 nm, represented by thefollowing Mathematical Formula 2:R _(in)=(n _(x) −n _(y))×d  [Mathematical Formula 1]R _(th)=(n _(z) −n _(y))×d  [Mathematical Formula 2] where, n_(x) is arefractive index in a direction in which the index is largest, in thefilm plane, n_(y) is a refractive index in a direction perpendicular tothe n_(x) direction, in the film plane, n_(z) is a refractive index in athickness direction, and d is a film thickness.
 9. The optical film ofclaim 1, wherein the optical film has an in-plane retardation value of 0nm to 10 nm, represented by the following Mathematical Formula 1, and athickness retardation value of −10 nm to 10 nm, represented by thefollowing Mathematical Formula 2:R _(in)=(n _(x) −n _(y))×d  [Mathematical Formula 1]R _(th)=(n _(z) −n _(y))×d  [Mathematical Formula 2] where, n_(x) is arefractive index in a direction in which the index is largest, in thefilm plane, n_(y) is a refractive index in a direction perpendicular tothe n_(x) direction, in the film plane, n_(z) is a refractive index in athickness direction, and d is a film thickness.
 10. The optical film ofclaim 1, wherein the optical film has a haze value of 1% or less. 11.The optical film of claim 1, wherein the optical film has a photoelasticcoefficient of 10 or less.
 12. The optical film of claim 1, wherein aheight from a hole produced on the optical film by dropping an ironsphere with a diameter of 15.9 mm and a weight of 16.3 g on a test filmis 600 mm or more, wherein the height from the hole refers to the heightfrom which the iron sphere was dropped.
 13. A liquid crystal displaydevice comprising the optical film of claim
 1. 14. The liquid crystaldisplay device of claim 13, wherein the liquid crystal display device ison VA mode.